I've got a dead Mission Cyrus Two amp, which was inherited from a mate a
couple of years ago. On looking inside, it appears that there are two TO220
packages which have had the tops blown off them, along with an 8-pin IC. The
part numbers, as best I can make out, are...

TDB 0137 SP
LM 317 SP
LF 353 DP

The 317 is a voltage regulator, and I'm guessing that the 0137 is the
negative equivalent of the 317. Does that sound right? I think the 353 is an
op-amp. The resistors adjacent to the TO220 packages still produce readings,
so I'm assuming that they're okay. I haven't powered it up to see if the PSU
is okay, and I haven't tested any other components (like o/p trannies).

I'm wondering if changing the blown devices might just effect a repair.
Before I get the soldering iron out, does anyone have a schematic for this
amp, or know where I can get one?


--
Wally
www.artbywally.com
www.wally.myby.co.uk

Wally wrote:
I've got a dead Mission Cyrus Two amp, which was inherited from a
mate a couple of years ago. On looking inside, it appears that there
are two TO220 packages which have had the tops blown off them, along
with an 8-pin IC. The part numbers, as best I can make out, are...

TDB 0137 SP
LM 317 SP
LF 353 DP

The 317 is a voltage regulator, and I'm guessing that the 0137 is the
negative equivalent of the 317. Does that sound right? I think the
353 is an op-amp. The resistors adjacent to the TO220 packages still
produce readings, so I'm assuming that they're okay. I haven't
powered it up to see if the PSU is okay, and I haven't tested any
other components (like o/p trannies).

I'm wondering if changing the blown devices might just effect a
repair. Before I get the soldering iron out, does anyone have a
schematic for this amp, or know where I can get one?

You can replace the TDB with the easier to find LM337. It soulds like a
nasty short somehwere to blow the regulators or more likly giving them a
rather high voltage to try and regulate. I would give the PSU a good
checking over before you blow another pair! The op-amp would require a +ve
and -ve supply so probably died before the regulator gave up!

Will

Will Reeve wrote:

You can replace the TDB with the easier to find LM337.

Good - I thought it might be from the same family (137/337). I'll track down
some 337s.


It soulds like
a nasty short somehwere to blow the regulators or more likly giving
them a rather high voltage to try and regulate.

I thought of a short at first, but I think the regulators are supposed to
have short-circuit protection, so I'm wondering if it's a problem with the
supply voltage.


I would give the PSU
a good checking over before you blow another pair!

That's exactly what I'm going to do - desolder the transformer first and see
if it's putting out believable AC. Then work forward if that's okay. If the
transformer's busted, I suspect the amp will be scrap.


The op-amp would
require a +ve and -ve supply so probably died before the regulator
gave up!

The only thing I know about its demise is that one channel went dead - no
bangs, flashes or smoke, according to the mate who then owned it. I agree
that the op-amp would have to blow before the regulators. :-)


--
Wally
www.artbywally.com
www.wally.myby.co.uk

Will Reeve wrote:

I would give the PSU
a good checking over before you blow another pair! The op-amp would
require a +ve and -ve supply so probably died before the regulator
gave up!

I switched it on the other night, and a capacitor went bang and flash. So, I
desoldered the transformer, measured it , and it looks okay - I get 30Vac
between the centre tap and each end of the coil. I also managed to track
down a schematic for a Cyrus One, which I gather uses similar circuitry.
I'll be having a look at separating the rectification smoothing parts of the
PSU from the rest of the amp so that I can test them without frying more
components.

Any idea what the o/p transistors are?


--
Wally
www.artbywally.com
www.wally.myby.co.uk